1. Field of the Invention
The present invention relates to a facsimile, a digital process copying machine, a still camera, a radiation imaging device, or other two-dimensional imaging devices and its imaging method, and particularly to an imaging device for forming an image by means of visible light or radiation and its imaging method.
2. Related Background Art
Conventionally, there have been put to practical use various types of imaging devices using a large-sized sensor made of two-dimensionally arranged image pick-up devices each having an Si single crystal sensor typified by a CCD sensor or an MOS sensor or each having a PIN sensor of hydrogenated amorphous silicon (hereinafter, referred to as a-Si). These imaging devices are used in not only forming an image of visible light, but also converting a radiation image to an electrical signal with the development of nuclear energy, radiation medical equipment, and nondestructive testing technique.
The S/N ratio in these types of equipment, however, is mostly double- or triple-digit and there has been no demand for any higher-digit S/N ratio. It is because the equipment is inconveniently subject to a memory limitation or a restriction in communication since there is no A/D converter suitable for digitizing an output of a high S/N ratio at a high precision or since a large amount of data remains after conversion, which results in a small demand for an imaging device having a high S/N ratio.
On the other hand, in recent years, development of a bulk memory or high-speed communication is remarkable and this enhances a demand for an imaging device having a higher 4- or 5-digit S/N ratio. Particularly, however, in an imaging device having a sample hold circuit in units of a line, a line noise extemporaneously comes to be mixed in a taken image due to an external environment in some cases. A source of the extrinsic noise, particularly in an X-ray imaging device, is an X-ray high-voltage power supply in a neighboring photo studio. It is unclear when and what timing the extemporaneous noise occurs and therefore the picture may be distorted by accident problematically. This problem has occurred also in a device having a reference potential provided for each column or row in a read circuit. In this manner, there has been a need for previously considering how to take measures against the extemporaneous noises as well as a device-specific noise caused by a variance of elements in a sensor panel or the like.
In view of these conventional problems, the present invention has been provided. Therefore it is an object of the present invention to provide an imaging device capable of obtaining high-quality image information with line noises reduced and its imaging method.